The present invention relates to reproduction circuits for use in magnetic recording/reproduction systems.
Hitherto, there has been known a magnetic reproduction circuit employing a Hilbert transform filter and a delay element, which circuit corrects reproduction signals read out of a magnetic recording medium having a magnetization component in its moving direction and a magnetization component perpendicular to the moving direction. Magnetic reproduction circuits of such type have been disclosed in, for example, Japanese Unexamined Patent Publication No. 231404/1987 and B. J. Langland "Phase Equalization for Perpendicular Recording", IEEE Trans. on Magn., Vol. MAC-18, pp. 1247-1249, 1982 (hereinafter referred to as "literature reference 1").
FIG. 8 is a block diagram showing the configuration of a reproduction circuit of this type, which comprises an input terminal 1 for reproduction signals fed from a magnetic head (not shown), a Hilbert transform filter 2, a delay element 3, an amplifier 4 of which amplification factor is -tan.alpha., an adder 5, an amplifier 6 of which amplification factor is cos.alpha., and an output terminal 7.
The operation of the reproduction circuit is to be explained. In this explanation there is used a reproduction waveform model given by the reciprocity theorem using a Karlqvist model as a magnetic field of a magnetic head and an arctangent function model as residual magnetization of a medium, as described in Robert I. Potter, "Analysis of Saturation Magnetic Recording Based on Arctangent Magnetization Transitions", J. Appl. Phys., Vol. 41, pp. 1647-1651, 1970 (hereinafter referred to as "Literature reference 2"). In this model a parameter .theta. is used, the ratio of a component in the medium-moving direction (hereinafter referred to as "longitudinal component") to a component perpendicular to the medium-moving direction (hereinafter referred to as "perpendicular component") is represented as cos.theta.: sin.theta..
Here, a reproduction signal e.sub.o (x) applied to the input terminal is represented by the equation (1): EQU e.sub.o (x)=e.sub.x (x).multidot.cos.theta.+e.sub.y (x).multidot.sin.theta.(1)
wherein a is magnetic transition width, d is pacing g is gap length and x is a variable distance from a point of magnetic transition. That is, the reproduction signal e.sub.o (x) represented by the equation (1) is the sum of the product of a longitudinal reproduction waveform e.sub.x (x) per unit magnetization by cos.theta. and the product of a perpendicular reproduction waveform e.sub.y (x) per unit magnetization by sin.theta.. The waveforms e.sub.x (x) and e.sub.y (x), respectively, are represented by the equations (2) and (3): ##EQU1##
FIGS. 7(a) to 7(c) are time charts showing a waveform of the reproduction signal e.sub.o (x), that of the longitudinal component e.sub.x (x), and that of the perpendicular component e.sub.y (x), respectively. As apparent from these figures, the longitudinal component e.sub.x (x) is even functional, while the perpendicular component e.sub.y (x) is odd functional. Consequently, the reproduction signal e.sub.o (x), or the sum of these components, is asymmetrical. The longitudinal component e.sub.x (x) and the perpendicular component e.sub.y (x) can be transformed to each other by Hilbert transform and the relationship therebetween is represented by the equations (4) and (5): ##EQU2##
Therefore, an output eh(x) as a result of the Hilbert transform of the reproduction signal e.sub.o (x) is represented by the equation (6): EQU e.sub.h (x)=-e.sub.x (x).multidot.sin.theta.+e.sub.y (x).multidot.cos.theta.(6)
As shown in FIG. 8, the parameter of the amplifiers 4 and 6 being set to .alpha.=.theta., this transformed output signal e.sub.h (x) is amplified by the amplifier 4 to give a signal, -tan.theta..multidot.e.sub.h (x), to which is then added by the adder 5 the reproduction signal e.sub.o (x) compensated by the delay element 3 for its delay produced by the Hibert transform filter 2 and amplifier 4, followed by amplification of the sum by the amplifier 6. This gives the output terminal a signal e.sub.c (x) resulting from the transformation of the signal into a waveform equivalent to the even functional waveform shown in FIG. 7(b) of the longitudinal component e.sub.x (x). The signal e.sub.o (x) is represented by the equation (7): EQU e.sub.c (x)=(e.sub.o (x)-tan.theta..multidot.e.sub.h (x)}cos.theta.=e.sub.x (x) (7)
Thus, the transformation of the signal into a even functional waveform makes it possible to simplify the reproduction signal processing.
In the above-mentioned conventional magnetic reproduction circuit using Hilbert transform filter, it is required to strictly control or establish the magnetic characteristics of the medium, recording/reproduction conditions of the system and the like so that the ratio of the longitudinal component to the perpendicular component is set within a range predetermined by a design value of the magnetic reproduction circuit. Stated otherwise, as the ratio departs from the range, a problem arises that the waveform cannot be corrected as required with remaining asymmetry. Further, if the reproduction circuit is used in a system employing a removable medium, the allowable design values for the reproduction circuit and succeeding circuits are required to increase correspondingly to variation in magnetic characteristics of media, which results in insufficient performance of the head and medium.
It is, therefore, an object of the present invention to overcome the foregoing problems and to provide a magnetic reproduction circuit with a circuit for calculating the ratio of a longitudinal component to a perpendicular component and an amplifier of which amplification factor is variable corresponding to the ratio, the reproduction circuit being capable of obtaining a reproduction signal e.sub.c (x) resulting from the transformation of a signal into a waveform equivalent to a even functional waveform of the longitudinal component e.sub.x (x) even when there is a variation in the magnetic characteristics of a magnetic medium, the intensity or distribution of a magnetic field of a head, or the like.